Overrode get_readonly_fields to make name readonly for existing object. Fixes #146. Also added field ordering.
Rewrote logic of clean() to validate by UID when re-activating, but validate by name when creating new.  Part of #146.
Merge branch 't146-prevent-name-edits' into m5-001-integration
Merge branch 'm5-001-integration' of github.com:gwu-libraries/social-feed-manager into m5-001-integration